1. Field of the Invention
The present invention relates to a battery unit comprising cells and a circuit board.
2. Description of the Related Art
Generally, cells are designed such that when the cell's internal pressure increases above a certain value due to gases produced by chemical reaction, for example in overdischarge, a safety valve opens to release gases from the cell. In this situation, sometimes an electrolyte leaks out of the cell through the safety valve together with gases. This phenomenon is called an electrolyte leak. In a battery unit comprising cells and a circuit board, when an electrolyte leak occurs and an electrolyte leaking out of the cells contacts the circuit board, it may cause problems, such as short-circuiting, to the circuit board by electrochemical migration, which may lead to a failure, heating, ignition and others.
In order to prevent the electrolyte leaking out of the cells from contacting the circuit board when an electrolyte leak occurs, it is often effective to arrange the circuit board so as not to be below the cells, for example. Arranging the circuit board so as not to be below the cells, however, restricts the freedom of the battery unit's internal layout to a great degree. As a result, a demand for downsizing the battery unit may not satisfactorily be met.
In a publicly-known example of prior technology intended to solve the above problem, a hole is provided in a wall of a cell container so that an electrolyte leaking out of cells is conveyed through the hole to a discharge hole and discharged from a battery unit through the discharge hole (see JP 2002-260606 A). In this prior technology, when an electrolyte leak occurs, the electrolyte leaking out of the cells is discharged from the battery unit by a route not contacting a circuit board, leading to a reduced possibility of the electrolyte leak causing problems such as short-circuiting of the circuit board.
In this prior technology, however, when an electrolyte leak occurs, the electrolyte leaking out of the cells is just discharged, or released from the battery unit through the discharge hole. There remains therefore a possibility that the electrolyte discharged dirties the surroundings.
The present invention has been made in view of the problems described above. An object of the present invention is to provide a battery unit in which an electrolyte leak is unlikely to cause problems such as short-circuiting of a circuit board, and in which an electrolyte leaking out of cells is unlikely to dirty the surroundings.